The objective of the proposed research project is to elucidate the intrinsic structure of the amygdala and discover how it develops. We have already examined the neurons of the lateral (L) and basolateral (BL) amygdaloid nuclei and have defined the cell types, the structure and orientation of their dendrites and the intranuclear distribution of their axons. The next step is to study in detail the afferent and efferent connections of individual neurons. Fluorescent tracing methods will be used to dtermine, for example, which neurons in L-BL send axons to frontal cortex and whether or not the same cells have collateral projections to hypothalamus or temporal lobe. Golgi, electron microscopic, anterograde degeneration, and horseradish peroxidase tracing methods will be applied to the same tissue. This will enable us to identify an individual neuron in L-BL and determine one of its projections and identify where a particular afferent fiber terminates on it. In addition to making these detailed observations in young, adult rodents, a carefully graded age series of brains will be studied with Golgi methods to investigate the normal, developmental history of amygdaloid neurons and their processes and how they change with age. A Golgi analysis of the basomedial and central amygdaloid nuclei will also be undertaken. All of these experiments and observations will provide the sort of detailed data that are necessary for designing and interpreting future experiments aimed at understanding how such variables as sensory experience, nutrition, and hormonal changes can affect the functioning of the amygdala that results in altered behavior. Structural changes caused by shifts in hormone levels may be related to differences in behavior that occur with puberty. Yet other changes in amygdaloid structure may be the basis for abnormal behaviors that include uncontrollable aggressive behavior. Structural changes during development might be significant in explaining retarded social behavior or the abnormal behaviors recognized in children as the pervasive developmental disorders.